Use an Optical to Stereo Phono converter such as this
These boxes are an active circuit i.e. they require power to work. This can either be from a wall socket adapter or from a USB cable. This one comes with the wall socket power supply. There'll be similar products with a USB power cable if that works better for you.
The output from the box is stereo phono. You need some long and thin but well-shielded phono leads to run around the room and connect to the stereo system. Most analogue audio cables have only basic shielding from interference. The short cables behind a stereo system aren't too exposed, so what little hum they pick up is masked by the audio signal, and so the shielding on these shorter cables is mostly adequate. When you start to run longer cables then they act more like an aerial: They radiate-out interference; we call this cross-talk. It's where you hear the signal from one channel faintly on the other i.e left on right and right on left. They also pick up radio waves generated by poorly shielded power supplies, TV and radio transmissions, certain types of electronic circuits yadda yadda yadda. Mostly this manifests as background hum.
Alternatives to running cables include:
- moving the stereo and TV together
- Bluetooth transmitter/receiver pairs - TX/RX - (sound quality takes a bit of a hit here and you have to watch out for lag in the sound - see aptX
lower down the page)
- radio link / video & audio senders (susceptible to wireless Wi-Fi B 2.4GHz interference and also sensitive to the emissions from your microwave oven)
- stereo audio over Cat5
This last one actually works pretty well. You're still running a cable, but this time only one (albeit, thicker at approx 5mm diameter) and you don't have to worry about shielding quality. Cat cables
make use of something called balanced line
or balanced signal pair
. Without boring you to death with the technical details, the boxes and cables work together to eliminate noise picked up along the cable length. The small domestic kits will run up to 100m without any significant noise. You'll still need the optical converter behind the TV.
Either cable solution isn't without its own issues though. There's work involved in running a cable, and aesthetics has to be considered. Hiding a Cat5 or a couple of 3mm diameter shielded audio cables isn't too difficult in a carpeted room, but it's more of a challenge if the room has wood or laminate flooring. There's also the question of what happens if the cable has to cross a doorway.
If cable still seems like the right way to go for you, but you're concerned about buying blind and then having hum issues after the hard work of installing has been done then drop me a line. I use these kind of cables regularly on commercial and domestic installations so I can sort you out with the right gear.
Bluetooth TX/RX kits
work by converting the incoming signal in to a data stream compatible with the Bluetooth transmission protocols. However, this signal conversion takes time. That means if you're watching the TV and have sound coming from the stereo speakers then there'll be a delay. If you were Bluetoothing from the phone to the car stereo then you wouldn't notice the time delay because there's nothing to measure it against. But as soon as you have a TV image then that all changes. People's lips move but the sound comes anywhere up to 2 seconds later.
Bluetooth was really designed for passing small amounts of data between devices near each other. It wasn't ever thought of as a means to transmit audio, but the convenience of it has been seized upon. Squeezing the large amounts of data in audio through such a small pipeline means there's a lot of compression too. That's not so important in the noisy environment of a car or with small desktop speakers with limited audio fidelity, but when you hear sound through a decent stereo then you'll probably notice the quality drop.
AptX is a technology to try to address those two issues. It uses a different CODEC to regular Bluetooth in an attempt to "not throw away as much of the sound", and the processing time is reduced too. However, it's still nowhere near as good as a wired connection both in quality and time.
There are two versions of AptX; the best has a latency of 35 milliseconds per device
. The standard version of AptX has 100ms, and again it's per device. For reference, 100ms is 1/10th of a second. That doesn't sound like much but in audio terms it's very noticeable. To put it in context, a Sky box has audio delay adjustable in 20ms steps, and that's considered quite crude; you'd definitely perceive a 20ms lag. Be careful if you decide to go down the Bluetooth route; yes, it's convenient and "high-tech" , but that doesn't mean it's the best audio solution.
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